Polarized absorption and fluorescence

Figure 6-8. b- and c-polarized absorption and fluorescence spectra in the range between 18000 cm and 19000 cm". The fluorescence peaks A and C correspond to the false origins O and O" identified in absorption. 

Figure 2. Polarized absorption and fluorescence emission P, polarizer A, analyzer.

The first example of using the [2+2] cycloaddition for crosslinking of organic semiconductor layers was reported in 1997 by Remmers et al. [10]. It was a derivative of poly-p-phenylene (PP) deposited by the Langmiur-Blodgett (LB) technique (Fig. 9.5(a)). Polarized absorption and fluorescence of the films was reported, but no OLED devices were fabricated. 

More recently, the polarized absorption and fluorescence spectra obtained at 4.2 K from an oriented 6T single crystal allowed the assignment of the lowest singlet electronic transition (located at 18360 cm" ) to the 1 transi-... 

Fig. 1 - polarized absorption and fluorescence emission. P = polarizer A = analyzer... 

The nature of the electronic states of carbazole and N-alkyl substituted derivatives has been established on the basis of quantum-mechanical calculations as well as by spectroscopic methods involving polarized IR and Raman spectra and polarized absorption and fluorescence emission spectra Four n n electronic transitions to singlet excited states have been predicted and observed in the 350-230 nm region which, in the Platt notation, are designated as - A ( 345 nm), L, <- A ( 295 nm), <- A( 265 nm)and Bt, <- A ( 240 nm) All these bands diplay... 

Linear absorption and fluorescence spectra for the series of symmetrical cationic polymethines with 5-butyl-7,8-dihydrobenzo[ /]furo 2,3 /lindolium terminal groups are shown in Fig. 14 for solvents of different polarity. It is known that the polarity of solvents can be characterized by their orientational polarizability, which is given by Af = (e- l)/(2e + 1) — (n2 - l )/(2n2 +1), where e is the static dielectric constant and n is the refractive index of the solvent [41], Calculated A/values... 

Additionally, note that the polarity of the solvent significantly affects not only the positions of absorption and fluorescence spectra but also the fluorescence quantum yields. The largest difference in quantum yield is observed for G19 (eight times larger in toluene) [86]. The effect of solvent polarity on quantum yield and fluorescence lifetime was investigated in mixtures of toluene and ACN (polarity range 0.013-0.306). Polarity dependent quantum yield and lifetime measurements are presented in Fig. 22. 

There are single- and multiparameter approaches for determining the polarity and separation of contribution of different interactions to the total effect of polarity on spectroscopic characteristics. They are based on different theories of solvatochromic shifts of absorption and fluorescence bands. 

A multi-parameter approach is preferable and the re scale of Kamlet and Taft (Kamlet et al., 1977) deserves special recognition because it has been successfully applied to the positions or intensities of maximal absorption in IR, NMR, ESR and UV-visible absorption and fluorescence spectra, and many other physical or chemical parameters (reaction rate, equilibrium constant, etc.). Such observables are denoted XYZ and their variations as a function of solvent polarity can be expressed by the generalized equation... 

Light absorption and fluorescence, FLUORESCENCE LIGHT POLARIZATION LIGHT SCATTERING... 

Electronic absorption and fluorescence excitation and emission spectra of phenazines were determined in several solvents of various polarities <1995SAA603>, and the effect of the solvent upon the spectral characteristics was studied. 

Spectroscopic measurements of solvatochromic and fluorescent probe molecules in room temperature ILs provide an insight into solvent inter-molecular interactions, although the interpretation of the different and generally uncorrelated polarity scales is sometimes ambiguous [23]. It appears that the same solvatochromic probes work in ILs as well [24], but up to now only limited data are available on the behavior of electronic absorption and fluorescence solvatochromic probes within ILs and IL-organic solvent mixtures. 

The variations of the simulated steady state solvatochromism, as a function of the polar solvent molarity, were found to be in good agreement with the experimental work of Krolicki et al. [4], both for absorption and fluorescence. The difference of Stokes-shifts between benzene and acetonitrile is 981 cm-1, compared to 1230 cm-1 obtained experimentally. These numbers are 870 cm-1 and 1910 cm-1, respectively, for methanol. 

The absorption and fluorescence spectra of DMABN-F4 in solvents of low and high polarity are depicted in Fig. 2. The corresponding spectra of DMABN are also presented for comparison. Both absorption and fluorescence spectra of DMABN-F4 are red-shifted with respect to those of DMABN (300 nm instead of 282 nm and 456 nm instead of 341 nm, in hexane). The bathochromic shifts of fluorescence upon fluorine substitution are consistent with a strong charge-transfer (CT) character of the emitting state. 

Related investigations have involved studies of the electronic, fluorescence and phosphorescence spectra1178 and the polarized absorption and linear dichroism spectra"79 of zinc porphyrins. 

An alternative approach to quantify polarity effects was proposed by Kamlet el al. [7], According to this approach the positions of the bands in UV-visible absorption and fluorescence spectra can be determined as... 

Fig. 5.4. Calculated fluorescence circularity rate under linear polarized excitation as dependent on squared electric field 2 for different absorption and fluorescence branches.

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